A truck is typically provided with a connector receptacle at the rear and the signal and brake lighting circuits of the truck are connected to the receptacle to provide a connection for energizing the signal and brake lighting circuits of a vehicle which is being towed. A light truck (one ton and under) is usually provided with a 4-position flat connector receptacle wired according to ASAE standard J1239. That is, the signal lght control system in the towing vehicle provides intermittent pulse type signals to connector position 3 when a left turn is signaled and to connector position 4 when a right turn is signaled. When the brakes are applied on the towing vehicle, the signal light control system applies continuous signals to connectors 3 and 4 for as long as the brakes are applied.
On the other hand, road farm implements are typically provided with 7-position connector plugs which connect with 7-position receptacles provided on tractors, these plugs being wired to ASAE standard J560b which requires that connector position 4 be connected to both brake lamps, connector position 3 be connected to the left turn signal lamp, and connector position 5 be connected to the right turn signal lamp. Thus, the pulse type signals appearing at positions 3 and 4 of the 4-position connector must be distinguished from the braking signals at these same positions if the implement lighting system is to be properly controlled.
A somewhat similar problem is raised by ASAE standard 279.10 (1996 revision of ASAE standard 279.9) for the lighting and marking of agricultural equipment when traveling on a public road. Tractors and self-propelled equipment must have two amber warning lights, visible from the front and rear, and flashing in unison at a rate of 60 to 85 flashes per minute. When turn signals are provided the amber warning lights must also serve as turn indicators. The amber light in the direction of the turn must flash and the amber light in the direction opposite the turn must become steady burning. A single 7-position receptacle must be provided, the receptacle conforming to ASAE J560 and having at least positions 1 (ground), 3 (left turn), 5 (right turn), and 6 (tail lights), wired for service.
For towed agricultural implements which obscure illumination of any flashing warning lamp or extremity lamp on a towing vehicle, ASAE 279.9 requires lighting on the implements. At least one tail light is required if the implement obscures a tail light of the towing vehicle. Wide implements or implements extending laterally of the towing vehicle or more than 10m behind the vehicle must have at least two amber flashing warning lamps which flash in unison with the warning lights on the towing vehicle and also serve as turn indicators.
The 1996 revisions are intended to provide enhanced lighting functions. For tractors and self-propelled equipment, these revisions specify that turn indicators must be provided. When a turn is signaled, the amber flashing warning lamp in the direction opposite the direction of turn is to be steady burning. The amber flashing warning lamp in the direction of turn must increase in flashing rate a minimum of 20 flashes per minute, so as to flash at a rate of at least 80 but no greater than 110 flashes per minute. In addition, the red tail lamp or an additional amber lamp must flash in the direction of turn and in unison with the amber flashing warning lamp.
If towed equipment obscures any tail lamp on the towing machine, ASAE 279.10 specifies that the towed equipment shall have two red tail lamps. If a flashing warning lamp on the towing machine is obscured, the towed equipment must have two amber warning lamps which flash in unison with the warning lamps on the towing machine. If a turn indicator on the rear of the towing equipment is obscured, the towed equipment must have turn indicators operating in exactly the same manner as the turn indicators on the towing equipment.
According to ASAE 279.10, positions 3 and 5 of the connector receptacle receive either a pulse type signal or a continuous signal depending on the direction of turn, whereas position 4 receives only a braking signal which is continuous for intervals the brakes are applied. Since the brake lamp in the direction of turn must flash until a turn signal is canceled, it is desirable to be able to determine the types of signals appearing at positions 3 and 5.
U.S. Pat. No. 5,498,929 discloses a system providing enhanced lighting functions on a towed farm implement. This system utilizes a relay to connect one end of both brake light filaments on the towed implement to ground when a turn is signaled, the relay coil being energized by the intermittent difference in voltage magnitude existing between the pulse type signal signaling the direction of turn and the continuous signal signaling the direction opposite the turn. As explained in the patent, the system is sensitive to timing differences between flasher signals as might occur when the flashers are controlled by separate relays in the lighting circuits of the towing vehicles, and an RC delay circuit may be provided to overcome this problem by delaying the energizing of the relay.